Research ship drills deep into seafloor

A JAPANESE research ship has drilled a 1.6-kilometre-deep hole in the sea floor while floating on 2 kilometres of ocean - making it the deepest hole ever drilled from a ship.

The Chikyu research vessel, operated by the Japan Agency for Marine-Earth Science and Technology, uses a technique known as riser-drilling, which recirculates viscous "drilling mud" to maintain pressure balance in the borehole.

According to Bill Ellsworth of the United States Geological Survey in Menlo Park, California, petroleum drilling on land and from stable ocean platforms regularly reaches depths of between 5 and 8 kilometres. The deepest land-based hole, drilled for research purposes on the Kola peninsula in Russia, goes down more than 12 kilometres, but drilling from a ship is a different matter, he says.